I have just downloaded a zip file which I am unable to open. When I have downloaded zip files in the past all I did was right click then I would get an option to extract all, this option has now vanished. The only option I get is to open it in Word. I am using Vista.
It might just be a corrupted download. Try downloading it again.
Alternatively, Vista's 'unzipping' software might not be available for some reason. Simply restarting your computer might fix the problem. If not, try running System Restore.
If none of that works, you could always use a free 'stand alone' program for extracting your files: http://www.izarc.org/